Salmonella has the ability to invade the cells of the intestine epithelium. This ability is largely dependent on the function of the products of a genetic locus inv, located at 59 minutes in the Salmonella chromosome. A number of genes have been identified in this locus and sequence homologies of the predicted gene products indicate that it is involved in epithelial cell membrane ruffling and bacterial internalization. The invF gene product is thought to be a transcriptional regulator, however it does not regulate other members of the inv locus. Then, the applicant will research its function by using a multidisciplinary approach involving Molecular Biology, Cellular Biology, Physiology, Classic Genetics, Immunology and Microbiology. A number of techniques to be used have been described by Dr. Galan and coworkers. Research on Microbial Pathogenesis, has been focused on getting a better understanding of the molecular mechanisms by which Salmonella spp. gain access to non-phagocytic cells. In recent years this has become in one of the most important fields of research that are allowing to obtain basic knowledge about an infectious microorganism and its relationship with the host. Based on this knowledge is being possible to design different strategies for the control and study of bacterial species that have an impact on human and animal health, mainly in developing countries. The specific aims are: To identify S. typhimurium genes whose expression is under the control of invF. To carry out a molecular and functional analysis of the gene(s) identified in the previous specific aim. To examine the effects of the purified product(s) on the invF-controlled gene(s) on cultured mammalian cells.